Which condition is marked by occupants expressing health complaints related to indoor air quality?

Sick Building Syndrome (SBS) refers to a situation where occupants of a building express health complaints that appear to be linked to the time spent in that building, although no specific illness or cause can be identified. Common symptoms of SBS include headaches, dizziness, respiratory issues, fatigue, and other general health complaints that arise in association with the building's indoor environment. The key aspect of SBS is that the symptoms often improve when individuals leave the building or are outside of it, indicating a relationship between the indoor environment and the occupants' health issues.

In contrast, Building Related Illness (BRI) is characterized by more defined, diagnosable illnesses that can be directly attributed to specific contaminants present in the indoor environment. Additionally, while the term "Indoor Air Quality (IAQ) issue" encompasses a broad range of problems and doesn't specifically imply occupant health complaints, Aspergillosis is a specific type of fungal infection that is not indicative of a broader syndrome affecting multiple occupants. Thus, Sick Building Syndrome is the most relevant choice for the condition marked by occupants expressing health complaints related to indoor air quality.